AC not resuming on engine restart

Discussion in 'Prius v Main Forum' started by djasonw, Oct 18, 2021.

  1. djasonw

    djasonw Active Member

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    Here’s a strange issue I seem to be having. I’ll preface this by saying my AC works perfectly. The blower motor is relatively new and all systems seem fine. Lately, after I turn the car off, I have to manually restart the AC. I’ve always set it and forget it and it resumed as it was from the prior drive. Now I have to hit the AUTO AC button to turn it on. It also reverts to 75° even though I have it set at 68°. (I like it cold). Any ideas? I can certainly live with it, but I’m really puzzled.


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  2. ChapmanF

    ChapmanF Senior Member

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    Sticking my finger in the wind and saying the first thing that comes to mind: I think there are two different power circuits that feed the A/C "amplifier" (an ECU by any other name...). One is powered only when the car is IG-ON or READY, and wakes it up, and the other is powered at all times, and holds its memory.

    This sounds as if the memory (often called B+) circuit is without power, so the ECU works fine when the car is ON or READY, but wakes up with fresh defaults every time it wakes up.

    I have not sought out a wiring diagram to check my guess though.
     
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  3. jzchen

    jzchen Senior Member

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    Besides @ChapmanF 's concern another possibility may be the 12 V is weak. Does this also happen to the last radio station set?

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  4. djasonw

    djasonw Active Member

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    My 12 volt battery was changed about a year ago. I actually think the first response (thanks) is on to something. I deliberately switched back on the car about a minute after I turned it off. It resumed the AC normally. I'm wondering if this issue is a precursor of things to come. I'll keep you all posted. Again, thanks for your input. It's greatly appreciated.

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